Abstract

Nonylphenol polyethoxylates (NPEOs) are common contaminants in the aquatic environment through their use as industrial surfactants and their discharge in wastewaters and effluents. In order to assess the bioavailability of NPEOs to fish, we studied the fate of two different oligomeric mixtures of NPEOs in adult roach Rutilus rutilus. Fish were exposed to [14C] radiolabelled NPEOs, averaging either 3 ethoxy units (NP3avEO) or 7 ethoxy units (NP7avEO), over a 4-day period in a flow-through aquarium. A method was developed to extract radioactive residues from soft tissues and analyse their composition by normal phase radio-HPLC and GC-MS. Radioactive residues were detected in all soft tissues of the roach dosed with either of the test mixtures, but the concentration of NPEO residues in each tissue were highest in fish exposed to the NP3avEO compared with the NP7avEO test mixture. Radioactive concentrations in roach dosed with 14C NP3avEO were highest in the bile at a mean concentration ± S.E. of 62 ± 3 µg/g wet weight, whereas concentrations in the liver, kidney and brain tissues ranged between 1 and 2 µg/g and concentrations in other soft tissues were between 0.1 and 0.7 µg/g. Analysis of the radioactive residues in bile of roach exposed to the NPEO test mixtures indicated that they were mainly metabolites including glucuronide conjugates, whereas in muscle, ovary and gill tissues they were a mixture of NP and short chain NPEO oligomers comprising 1¿4 ethoxy units. This study suggests that short chain NPEO oligomers are taken up via the gills and accumulate in tissues such as gonads which are sensitive to endocrine disruption, whereas waterborne NPEOs containing more than 4 ethoxymers are not bioavailable to roach.